The drawing speed of welding wire is seriously affected and fracture of welding wire is easy to happen due to high nitrogen content of the ER70S-6 welding wire steel so that user requirements cannot be met. In order to reduce the nitrogen content in steel, the technological process of converter steelmaking is studied systematically as well as the factors influencing nitrogen content in steel and control measures are discussed. In the paper, the dissolution mechanisms of nitrogen in steel are analyzed by thermodynamics, restricted links of nitrogen removal are analyzed and studied by dynamics as well as the influences of sulfur content in molten iron in furnace, slag charge in top of converter, times of spot blowing for converter and maintenance of tap hole of converter on nitrogen content and corresponding measures for controlling nitrogen content in the technological process of steelmaking are studied based on the thermodynamic analysis and dynamic mechanical analysis.

The contents of calcium oxide, silicon dioxide, magnesium oxide, phosphorus and sulfur in metallurgical lime are determined by means of fusion sample preparation-X-ray fluorescent spectrometry. The optimum experimental conditions are determined by analyzing the influences of such factors as fusing agent, release agent, dilution ratio, melting time and temperature on the determination results. Meanwhile, the calibration curves of each element are drawn with standard samples and self-made standard samples with appropriate contents as well as the correlation coefficients are all over 0.999. The experimental samples are determined with test methods. The results showed that the measured and theoretical values of each element could meet the requirements of tolerances as well as relative standard deviations of each element in precision experiment were all less than 5%, which was with higher accuracy and precision. The operation of loss on ignition is not needed for preparing fusion samples in this method so that the experimental processes are greatly simplified and work efficiency is effectively improved, which is with certain promotional and application values.

In this paper, the continuous cooling transformation (CCT) curve of X80 pipeline steel researched and developed in laboratory is determined. The determination results showed that the ideal microstructure of X80 pipeline steel could be obtained when cooling rate was 5~30 ℃/s, which was granular bainite + ferrite bainite + a small quantity of martensite/austenite island; the microstructure transformation was basically completed when finish cooling temperature was 450 ℃. The determination of CCT curve could provide references for subsequent optimization of composition design, establishment of process parameters and control of microstructure.

With the environmental protection and production limitation, the output of sinter is becoming increasingly tense after 1^# and 2^# sintering machines in 1^# sintering workshop are not in the production sequence as well as the addition of large proportion of pellets into blast furnace has become new development trend of iron-making. During this test, 5^# blast furnace is with trouble free operations through regulating charge level, adjusting central coke quantity and discharging sequence of feed zone, optimizing parameters of tuyere and area of inlet air, increasing heat reserve of hearth, adjusting and controlling basicity of slags as well as actively coping with various changes of furnace conditions after increase the proportion of pellets. The smelting production is successfully realized in the 1 500 m³ blast furnace of Baotou Steel with structure of furnace charge of large proportion of pellets and use ratio of pellets reaches 52%, so the fuel ratio is stable with a slight decline.

The frequent quality defect of corner crack for casting blank of carbon structural steel with conventional composition design of medium carbon and low manganese seriously affects the hot charge rate of products. With the original equipment and working conditions, composition optimization design is carried out. The mechanical properties of products are ensured through replacing part of C with microalloying element Ti as well as replacing solution strengthening with fine-grain strengthening and precipitation strengthening. Meanwhile, the high temperature plasticity and corner crack of casting blank are improved through liquation of second phase particle for TiN with the high temperature of Ti microalloying to fix free nitrogen atom in liquid steel. The rate of corner crack for carbon structural steel Q235B with new composition design is controlled effectively through the evaluations of mass production and applications.

In this paper, the effects of replacing iron ore concentrate of Inner Mongolia Autonomous Region with finely ground super special powder on production process and properties of pellet are systematically investigated based on the configuration of raw materials of producing acid pellet with the process of traveling grate-rotary kiln-rotating annular cooler of Baotou Steel. Meanwhile, the maximum proportion of Barun concentrate in producing pellet is explored based on the characteristics of low sulfur for finely ground super special powder. The results showed that the proportion of bentonite could be reduced obviously by adding the finely ground super special powder into pellet of Baotou Steel. When the proportion of finely ground super special powder is 10%, proportion of bentonite could be reduced from 2.0% to 1.2%, which is a significant reduction. When the proportion of finely ground super special powder is 5%~20%, performance indexes of green pellets and dry pellets could all meet production requirements of pellets. Under the condition of calcination temperature of 1 220~1 240 ℃, the compressive strengths of finished product, oxidized pellets prepared with different proportions of finely ground super special powder all reach over 2 500 N and reduction swelling rate is lower than 20%, which could meet the requirements of blast furnace production. It is suggested to produce pellets with the configuration of iron charge of 10% finely ground super special powder+50%~60% Barun concentrate+30%~40% iron ore concentrate of Inner Mongolia Autonomous Region for the process of traveling grate-rotary kiln-rotating annular cooler considering the grade of pellets and content of Al₂O₃. Under the raw material condition of 10% finely ground super special powder and 1.2% bentonite, the maximum proportion of Barun concentrate could reach 60%.

The timely pipeline dredging for long distance slurry pipeline could effectively ensure the safe operations of high pressure pipeline system. For the long distance high pressure slurry pipeline with the inner diameter of Φ212.75 mm, such 5 positioning tube cleaners of 3 types as the soft tube cleaners of Φ205 mm and Φ209 mm, soft descaling tube cleaners of Φ205 mm and Φ209 mm as well as four cup tube cleaners of Φ212 mm are adopted for descaling inside pipelines. For the slurry pipeline before dredging, the water discharge was 230.45 m³/h and outlet pressure of main pump was 1 150.7 kPa, while after dredging, the water discharge was 303.13 m³/h and outlet pressure of main pump was 1 115.2 kPa under the same condition of transporting slurry so that the flow of pipeline is increased by 31.54% and outlet pressure of main pump is reduced by 3.09%. The transportation capacity of pipeline could be effectively improved and outlet pressure of main pump could be reduced with the successful applications of dredging for slurry pipeline on site, which could be as important references for descaling long distance slurry pipeline.

The development and trial production of high corrosion-resistant products with Zn-Al-Mg coating for photovoltaic applications are carried out after transform Zn-Al-Mg production line of Baotou Steel. The microstructure of coating for Zn-Al-Mg products is analyzed, neutral salt spray test and surface defects of the products with Zn-Al-Mg coating are analyzed, controlled and studied. The analysis results showed that the microstructure of the coating was composed of Zn-rich phase, ternary eutectic phase of Zn/MgZn₂/Al and binary eutectic phase of Zn/MgZn₂ as well as the elements of Al and Mg were with uniform distribution in the coating; the neutral salt spray test results showed that the products with Zn-Al-Mg coating manufactured by Baotou Steel were with good corrosion resistance, processability, formability and self-healing ability of notch. The trial production results showed that the process control of Zn-Al-Mg production line of Baotou Steel was stable, stable batch productions of products with Zn-Al-Mg coating were realized, qualified rate of products reached 95.33% and yield reached 97.84% so that all performances could meet the technical requirements.

The hardness of hardened layer for rails after quenching is with hardness gradient and it is difficult to accurately calculate the threshold value ΔK_th of fatigue crack growth for rails. In the paper, the detection of threshold value ΔK_th is carried out through software optimization based on the fatigue crack growth software. The threshold values ΔK_th of U75V and U71Mn quenched rails with different stress ratios are obtained by national standard method and actual measurement method respectively. As a result, the threshold values ΔK_th of quenched rails obtained by actual measurement method are more accurate through comparative analysis of data.

The continuous cooling transformation (CCT) curves of Q1100D steel in cooling process are obtained through the thermal simulation of welding process with Gleeble-3800 testing machine. The microstructure and properties of welded joints under different heat inputs are tested with such methods as the Y-slit welding cold crack test, metallographic analysis and mechanical performance test. The results showed that the ultra high strength steel Q1100D for lifting arm of heavy machinery of Baotou Steel was with better cold check resistance. It could be welded without preheating at room temperature with the condition of a little heat input; with the condition of greater heat input, cold cracks are not observed on the surface and cross section, which indicates that Q1100D steel plate is with good cold check resistance. The evaluation results of comprehensive mechanical and structure properties of the joint indicate that the Q1100D steel plate with thickness of 14 mm is with optimum mechanical properties (tensile, bending and impact) of welded joint under heat input of 1.05 kJ/mm.